Intermittent feed conveyers comprising an article transfer belt and two or more parallel shaft drums about which the belt is located are known in the industry. Such apparatuses are used to transfer a work piece through a series of positions at which a number of operations may be carried out upon the work piece. In order to transfer each work piece from one work station to the next work station, it is necessary to intermittently drive the belt holding the work pieces a predetermined distance which corresponds to the spacing of the work stations. To accomplish this, the belt is rapidly accelerated from a stationary condition, transported a predetermined distance, and rapidly decelerated to a stationary condition, thereby locating the work piece at the next station. In order to achieve the high production speeds necessary in such apparatuses, it is extremely critical that the belt locate the work piece precisely at each work station. To achieve the necessary precision, no slippage can be allowed between the driven drum and the belt.
In U.S. Pat. No. 3,231,065 to Kaminski, et.al., a feeding apparatus is disclosed having a stainless steel belt which has sprocket holes along at least one edge of the belt. The belt is driven by a drum which has a sprocket disc attached to the drum. The teeth of the sprocket disc extend into the sprocket holes along the edge of the belt, thus preventing relative motion between the metallic belt and the drum. The belt also has apertures in which the articles can be seated in order to be carried by the belt. The articles which are particularly disclosed are beverage can ends.
While the apparatus of U.S. Pat. No. 3,231,065 has generally proven to be satisfactory, problems have arisen with the use of a metallic belt. Belts were found to fail in service due to cracks which propagated in the belt from the sprocket holes into the article carrying apertures. The failures occur because the fatigue limit, in terms of number of bending cycles around the drums, has been reached.
In response to the problems of metallic belts, the prior art also developed along the lines of fabric impregnated with neoprene or the like which had non-stretchable elements embedded therein. However, as with the metallic belts, a non-stretchable, non-metallic belt must also not slip with respect to the driven drum. To prevent slippage, various configurations have been devised.
One such configuration is disclosed in U.S. Pat. No. 3,812,953 to Maschke. In Maschke, a plurality of radially extending plugs are arranged on the peripheral surface of the driven drum, as well as on the peripheral surface of the idler drum. The plugs are arranged and configured to fit snugly into the article feeding apertures formed in the belt. The plugs drive the belt in unison with the rotation of the driven drum, while maintaining the relative position of the belt with respect to the drum, thereby preventing slippage. As was disclosed therein, the belt was anticipated to be either metallic or non-metallic, non-stretchable.
A major problem occurs with the use of radially extending plugs in combination with a non-stretchable, non-metallic belt. A non-metallic does not possess the bearing strength necessary to drive the belt via the plugs. When used in this combination, the non-metallic belt prematurely fails due to over stressing the belt. Furthermore, when the force used in a driving non-metallic belt is sufficient to drive the belt via the plugs, the force is also sufficient to allow the plugs to "flair" the belt openings. This "flairing", or stretching of the belt openings, results in positioning errors due to the localized deformation of the belt openings. This is particularly noticeable at the high intermittent speeds at which such apparatuses operate.
U.S. Pat. No. 4,289,231 to Kaminski discloses the use of low inertia drums in combination with a substantially non-stretchable belt which has inwardly projecting teeth that mesh with axially aligned sprocket teeth that are located about the periphery of the driving drum. While this represents one method of maintaining the accuracy necessary to successfully operate such apparatuses, the art is continually seeking to improve the performance and reliability of the apparatuses.
Forming axial teeth, as well as manufacturing the low inertia drums as disclosed in U.S. Pat. No. 4,289,231, is costly. Furthermore, there is a need in the art to reduce the tension induced in the belt by the take up drum to as low a level as is practically possible in order to extend the life of the non-metallic, non-stretchable belt. To these ends, the present invention offers significant improvements over the prior art.